1. FIELD OF THE INVENTION
The present invention relates to a cartridge-type magnetic tape changer in which one of a plurality of cartridge-type magnetic tapes contained in a magazine is loaded from the magazine into a magnetic tape unit and, after being ejected from the magnetic tape unit, is loaded back into the magazine.
2. DESCRIPTION OF RELATED ART
For recording desired information onto a magnetic tape ("MT" hereinafter) with a MT unit or reproducing the information recorded on an MT with the MT unit, a cartridge-type magnetic tape (hereinafter "cartridge") is loaded into the MT unit or taken out of the MT unit manually by an operator. To load/unload multiple cartridges sequentially for data or information recording or reproduction, cartridge changers have recently been proposed that have a magazine containing multiple cartridqes. Such cartridge changers are designed so that a certain one of the cartridges selected among the multiple cartridges contained in the magazine can be automatically loaded into the MT unit, and after being ejected from the MT unit, can be automatically returned into the same place in the magazine. One of these type of cartridge changers is disclosed in, for example, Japanese Unexamined Patent Publication No. 60-50740. According to this type of changer, the magazine has a plurality of cartridges that is fixed on a belt that extends between a drive roller and a driven roller, and the magazine is sequentially moved by the belt as the drive roller is driven in stepwise movement by a roller gear type transmission mechanism. The magazine is driven by the belt to a predetermined position at which one of the cartridges in the magazine is loaded into the MT unit. Problems, including belt slipping, elongation of the belt and the like lead to a possible failure in accurate positioning of the magazine. Further, the belt deteriorates over time so that there is a possibility of belt failure.
In the cartridge changers of the aforementioned type, a device is provided for detecting whether or not a certain one of the cartridges in the magazine is at the position in which it is to be loaded into the MT unit. Once it is in this position, the cartridge is loaded into the MT unit. Whether the cartridge is at the loading position or not can be detected by photoelectric detecting methods, for example. One such method is known from Japanese Utility Model Unexamined Publication No. 61-79856. In implementing this method, however, the length of the optical path between the light emitter and the photodetector of the photoelectric sensor must be larger than the length between the lateral sides of the cartridge. This is disadvantageous in that it is difficult to adjust the alignment between a light emitter and photodetector spread this far apart, and therefore the device is likely to malfunction.
Cartridge changers of the known type suffer from a further disadvantage in that while a certain selected cartridge is being automatically loaded and unloaded with respect to the MT unit, the operator cannot take out or replace any of the other cartridges from the magazine. Moreover, any cartridge not set in the magazine, but set directly into the cartridge changer, cannot be automatically supplied into the MT unit. Therefore, the cartridge-type magnetic tape changers of the prior art are inconvenient for an operator's use.